Document U.S. Pat. No. 7,488,088 B2 describes a light emitting diode lighting device, an LED lighting device for short, and a method that produces high intensity and spatially uniform white light in the near and far fields in a reduced package size that does not significantly heat the surrounding environment, wherein the white light is produced by using a phosphor layer in conjunction with at least one LED.
In different phosphor converted LED applications, such as in camera flash, and in general illumination applications, constant color point as a function of angle is desirable. A phosphor converted light source without a high collimation, such as an LED, shows a strong angular dependence of color point. This is due to the fact that the path length of the pump light in the phosphor typically depends on the angle of incidence while emission from phosphor typically shows a Lambertian distribution. The pump light, for instance blue LED light emitted by an LED 1, falls onto the ceramic or phosphor 2, respectively, as shown in FIG. 1. At larger angles the pump light shows a longer path length defined by the equation d/cos(Θ), where d is the thickness of the phosphor 2 and Θ is the angle of incidence of the blue pump ray. This situation is depicted in FIG. 1.
This effect results in blue and yellow light characterized by different angular distributions as shown in FIG. 2. In FIG. 2 it can be seen that emission of yellow light 6 from a phosphor 2 shows a Lambertian angular distribution whereas the initial Lambertian distribution of blue pump light 7 is altered such that the angular distribution becomes narrower after going through the phosphor 2.
In order to decrease losses, different solutions have been proposed in the prior art. However, these suggestions lead to reduced system efficiency while providing a possibility to achieve an almost constant color point. For instance, such a phosphor 2 can be made highly scattering which leads to the fact that a large amount of light is back scattered and lost in the phosphor converted light source system which is pumped by an LED 1 as shown in FIG. 3a. Another solution is placing a blue reflector 3 on top of the phosphor 2. However, a disadvantage of this solution is losing light in the phosphor converted light source system as a result of back reflection of the blue reflector 3 as shown in FIG. 3b. 
Furthermore, there are applications, such as automotive lighting, where more complicated angular light color distribution is needed for comfort and safety. This is very difficult to obtain in a simple way by using LEDs.